The invention relates to spreading devices used in trawl fishing and seismic survey operations, generally referred to as trawl doors, otterboards, deflectors, vanes or paravanes herein after also referred to as a “spreading device”.
Trawl doors in general, are used for demersal, semi-pelagic and pelagic fishing and paravanes are used for seismic surveys; they have the same basic purpose and can be of the same construction. The main purpose of trawl doors is to control opening of the fishing trawl to optimize catching performance of the complete fishing gear. The main purpose of paravanes is to spread the seismic system with a number of streamers behind a vessel.
Trawl doors are used to open a system of fishing gear. They are set from the vessel to the sea with its components connected between them. The doors spread out to each side from the vessel and generate a distance so the components, namely the fishing trawl, wires and cables herein after referred to as a “system”, are in optimal fishing conditions. A trawl door is connected to a steel wire cable or a synthetic rope leading from the vessel and the fishing net is connected to the trawl door in the opposite direction with another set of steel wire cables or synthetic ropes. Trawl doors are used in pairs were the trawl door on the right side is called “starboard door” and the trawl door on the left side is called “port side door”.
Paravanes or vanes are used to spread a system of streamers for a seismic survey. They are also used in pairs and are set from the vessel in a similar way as trawl doors to pull the streamers to each side of the vessel. Paravanes are almost without an exception, connected to synthetic ropes leading from the vessel and the seismic system, between the streamers and other components are also connected with synthetic ropes.
Basically, trawl doors and paravanes have the same purpose, to spread and hold the components in position between them.